1. Field
Exemplary embodiments of the present invention relate to a nonvolatile memory device and a method of fabricating the same, and more particularly, to a three-dimensional (3-D) structured nonvolatile memory device in which a plurality of memory cells are stacked in a vertical direction over a substrate and a method of fabricating the same.
2. Description of the Related Art
A nonvolatile memory device retains stored data although the power is not supplied. A variety of nonvolatile memory devices, such as flash memory, are being widely used.
As the improvement of the degree of integration of two-dimensional (2-D) structured nonvolatile memory devices with memory cells that are formed over a semiconductor substrate in the form of a single layer has reached the limit, there has been proposed a 3-D structured nonvolatile memory device in which a plurality of memory cells is formed along channel layers in a vertical direction over a semiconductor substrate. More particularly, the 3-D structured nonvolatile memory device is mainly divided into a structure having a straight-line type channel layer and a structure having a U-shaped channel layer.
In the structure having a U-shaped channel layer, a pipe connection transistor is used to couple memory cell strings. However, there is a concern in that electric resistance may increase, because the gate electrode of the pipe connection transistor (hereinafter referred to as a pipe connection gate electrode) is mainly made of polysilicon. Furthermore, a process margin may not be sufficient, because the pipe connection gate electrode may be damaged in a subsequent etch process for forming slits over the pipe connection gate electrode.